Field choppers, row-crop harvesters and like machines for recovering forage crops, corn and silage-making crops from a planted site can be of the self-propelled, drawn (towed) or tractor-mounted type.
In the first case, the vehicle chassis or frame not only carries the mouth of the machine together with any cutting devices which may be required and/or any crop pickup elements for retrieving a previously cut crop, but also includes a prime mover, especially an internal combustion engine, which provides motive power for the wheels of the machine as well as for the mechanisms cutting or lifting the crop, transporting the crop rearwardly and/or laterally, chopping the crop if desired, and ejecting the crop, e.g. into a forage wagon which can be drawn behind the harvesting machine.
When drawn or towed harvesting machines are used, however, they generally are pulled from the drawbar of a tractor by a tow bar which is pivotally connected to a drawbar by a pin and which also may be pivotally connected to the chassis or frame on which the wheels of the machine are mounted. Such machines are generally of two types, namely, with or without a prime mover.
In the first type, a prime mover is provided upon the frame or chassis and drives the cutter and/or crop pickup, any crop conveying chains, belts, drums or screws, a chopper or crusher if desired, and the blower. Again the silage wagon can be attached behind or alongside the drawn machine.
When, however, a prime mover is not provided upon the chassis or frame, the mechanism carried by the latter is generally driven from the power takeoff shaft of the tractor, e.g. by a connecting shaft having a pair of universal joints and which may be extensible, telescoping or splined, to allow a variable distance to be maintained between the harvesting machine and the tractor.
With towed or drawn machines, it is frequently necessary to establish a predetermined relationship between the axis or center of the harvesting machine and the axis or center of the towing tractor for various reasons. For example, for road transport of the harvesting machine it is desirable that the harvesting machine be disposed directly behind the tractor. This configuration is a disadvantage in most types of crop harvesting, since the tractor should travel over the region of a previous swath or over previously harvested ground while the machine is disposed laterally thereof to encounter the standing or previously mown crop. In this latter state, the center of the machine can be significantly offset from the center of the tractor.
Mention should also be made of the fact that it is known, in self-propelled machines particularly, to provide means for automatically aligning the mouth of the machine with the crop material to be harvested. For example, harvesting machines have been provided heretofore with means for sensing the crop and adjusting the mouth laterally of the direction of travel.
It is also known to use chopper harvesters carried by an agricultural tractor. Steering corrections by the driver of the tractor then act directly upon the forage harvester. The correction of lateral deviations and driving along the row to be harvested are thus relatively easy.
However in this case there are limits to the size of the harvesting machine used. Automatic lateral guidance is not provided.
Mention can also be made of a system described in German Democratic Republic Pat. DD-PS 32 123 to secure a tool carrier, which is laterally displaceable by a hydraulic cylinder, on the three-point hitch of an agricultural tractor.
Laterally of the tractor a forwardly extending feeler is secured on the tool carrier. This feeler slides along plant rows and is pivoted mechanically in the case of deviations. Thus a voltage divider mounted on the same spindle is displaced. This divider is connected with a second voltage divider to form a bridge. The center taps of both are connected with an amplifier which amplifies the differences between the bridge values and transmits them to the electromagnets of the hydraulic control slide member of a multi-way valve. Thus the inflow and outflow of pressure medium in the bilaterally charged (double acting) hydraulic cylinder is regulated.
This system is likewise used only in implements carried by the tractor. Moreover in the case of a forage chopper harvester it is hardly suitable since by reason of its size and weight such a harvester can only be laterally shifted on a tool carrier with difficulty.